Plasmonic surface-scattering elements and metasurfaces for optical beam steering

Abstract

Systems and methods are described herein for an optical beam-steering device that includes an optical transmitter and/or receiver to transmit and/or receive optical radiation from an optically reflective surface. An array of adjustable plasmonic resonant waveguides is arranged on the surface with inter-element spacings less than an optical operating wavelength. A controller applies a pattern of voltage differentials to the adjustable plasmonic resonant waveguides. The pattern of voltage differentials corresponds to a sub-wavelength reflection phase pattern for reflecting the optical electromagnetic radiation. One embodiment of an adjustable plasmonic resonant waveguide includes first and second metal rails extending from the surface. The metal rails are spaced from one another to form channel therebetween. An electrically-adjustable dielectric is disposed within the channel.

What is claimed is: 
     
       1. A method for transmitting a steerable reflected optical beam, comprising:
 transmitting, via a transmitter, optical electromagnetic radiation to a reflective surface; and 
 adjusting a reflection phase for each of a plurality of adjustable plasmonic resonant waveguides to modify a reflection pattern of the transmitted optical electromagnetic radiation, wherein the adjustable plasmonic resonant waveguides are configured to convey plasmons and are arranged on the reflective surface with inter-element spacings less than an optical operating frequency of the adjustable plasmonic resonant waveguides. 
 
     
     
       2. A method for receiving a steerable reflected optical beam, comprising:
 adjusting a reflection phase for each of a plurality of adjustable plasmonic resonant waveguides configured to convey plasmons, wherein the adjustable plasmonic resonant waveguides are arranged on the reflective surface with inter-element spacings less than an optical operating frequency of the adjustable plasmonic resonant waveguides; and 
 receiving, via a receiver, optical electromagnetic radiation from the reflective surface that is modified by a reflection pattern corresponding to the reflection phases of each of the plurality of adjustable plasmonic resonant waveguides. 
 
     
     
       3. An apparatus, comprising:
 a surface; and 
 a plurality of adjustable plasmonic resonant waveguides to convey plasmons, the adjustable plasmonic waveguides extending vertically from the surface and arranged on the surface with inter-element spacings less than an optical operating wavelength of the apparatus. 
 
     
     
       4. The apparatus of  claim 3 , wherein each of the plurality of adjustable plasmonic resonant waveguides comprises an electrically-adjustable dielectric and at least one plasmonic metal rail. 
     
     
       5. The apparatus of  claim 4 , wherein the electrically-adjustable dielectric of each of the plurality of adjustable plasmonic resonant waveguides is disposed within a channel between adjacent plasmonic metal rails. 
     
     
       6. The apparatus of  claim 5 , wherein adjacent adjustable plasmonic resonant waveguides share a common plasmonic metal rail, such that two adjacent adjustable plasmonic resonant waveguides are formed with:
 a first electrically-adjustable dielectric disposed between a first plasmonic metal rail and a second plasmonic metal rail; and 
 a second electrically-adjustable dielectric disposed between the second plasmonic metal rail and a third plasmonic rail. 
 
     
     
       7. The apparatus of  claim 3 , wherein the surface comprises a dielectric substrate with a plurality of copper patches embedded therein, wherein one of the copper patches is positioned beneath a channel of each of the adjustable plasmonic resonant waveguides. 
     
     
       8. An optical beam-steering device, comprising:
 an optical electromagnetic radiation converter to convert between electric power and optical electromagnetic radiation; 
 a surface to reflect the optical electromagnetic radiation; and 
 a plurality of adjustable plasmonic resonant waveguides arranged on the surface with inter-element spacings less than an optical operating wavelength of the device to convey plasmons and selectively apply a sub-wavelength reflection phase pattern to the optical electromagnetic radiation. 
 
     
     
       9. The device of  claim 8 , wherein the surface comprises an optical reflector to reflect optical electromagnetic radiation within an operational bandwidth that includes the optical operating wavelength of the device. 
     
     
       10. The device of  claim 9 , wherein the optical reflector comprises an electrically conductive reflector. 
     
     
       11. The device of  claim 10 , wherein the electrically conductive reflector comprises a layer of metal. 
     
     
       12. The device of  claim 11 , wherein the layer of metal has a notch beneath each of the adjustable plasmonic resonant waveguides. 
     
     
       13. The device of  claim 8 , wherein the surface comprises a plurality of optically reflective patches. 
     
     
       14. The device of  claim 8 , wherein each of the plurality of adjustable plasmonic resonant waveguides comprises:
 a first plasmonic metal rail extending to a first height from the surface; 
 a second plasmonic metal rail extending to a second height from the surface,
 wherein the first and second plasmonic metal rails are spaced from one another to form a channel therebetween; and 
 
 an electrically-adjustable dielectric disposed within at least a portion of the channel. 
 
     
     
       15. The device of  claim 14 , wherein each of the plurality of adjustable plasmonic resonant waveguides further comprises:
 electrical contacts to receive an applied voltage differential to the first and second plasmonic metal rails, 
 wherein application of a first voltage differential to the first and second plasmonic metal rail corresponds to a first reflection phase, and 
 wherein application of a second voltage differential to the first and second plasmonic metal rail corresponds to a second reflection phase. 
 
     
     
       16. The device of  claim 15 , wherein the adjustable plasmonic resonant waveguides are arranged in a one-dimensional array perpendicular to a length of the first and second plasmonic metal rails. 
     
     
       17. The device of  claim 8 , wherein the adjustable plasmonic resonant waveguides are arranged in rows and columns on the surface to form an M×N array, where M corresponds to the number of rows and N corresponds to the number of columns. 
     
     
       18. The device of  claim 17 , further comprising a matrix circuitry indexed by row and column to address each of the adjustable plasmonic resonant waveguides. 
     
     
       19. The device of  claim 8 , wherein each of the plurality of adjustable plasmonic resonant waveguides comprises an electrically-adjustable dielectric and at least one plasmonic metal rail. 
     
     
       20. The device of  claim 19 , wherein the electrically-adjustable dielectric of each of the plurality of adjustable plasmonic resonant waveguides is disposed within a channel between adjacent plasmonic metal rails. 
     
     
       21. The device of  claim 19 , wherein each of the plurality of adjustable plasmonic resonant waveguides comprises two plasmonic metal rails spaced from one another to form a channel therebetween, wherein the electrically-adjustable dielectric is disposed within the channel between the two plasmonic metal rails. 
     
     
       22. The device of  claim 21 , wherein the channel between the two plasmonic metal rails of each of the adjustable plasmonic resonant waveguides corresponds to a fundamental harmonic mode of frequencies within an optical operating bandwidth of the device. 
     
     
       23. The device of  claim 21 , wherein each of the plasmonic metal rails of each of the adjustable plasmonic resonant waveguides extends from the surface to a height corresponding to an Nth order harmonic mode of frequencies within an optical operating bandwidth of the device, such that N magnetic field antinodes can be realized within the channel between the surface and tops of the plasmonic metal rails. 
     
     
       24. The device of  claim 21 , wherein each of the two plasmonic metal rails of each of the adjustable plasmonic resonant waveguides each have a length corresponding to an Nth harmonic mode of frequencies within an optical operating bandwidth of the device, such that N magnetic field antinodes can be realized along the length of the channel between the two plasmonic metal rails, where N is a numerical value. 
     
     
       25. The device of  claim 21 , further comprising a controller to selectively apply a pattern of voltage differentials to plasmonic metal rails of each of the plurality of adjustable plasmonic resonant waveguides, wherein the pattern of voltage differentials corresponds to (i) a pattern of indices of refraction of the electrically-adjustable dielectric of each of the plurality of adjustable plasmonic resonant waveguides, and (ii) a reflection pattern of a wave of optical electromagnetic radiation incident on the plurality of adjustable plasmonic resonant waveguides.